Which weather model is most accurate in Boston?
Boston, Massachusetts · daily high temperature · trailing 30 days · refreshed at most every 6 hours
Every day, The Spread archives what each major weather model predicted for Boston at 1-, 3-, and 7-day leads, then scores those forecasts against ERA5 reanalysis once the day has happened. This page covers the trailing 30 days (2026-07-06 to 2026-08-05), for daily high temperature.
One day out, ECMWF IFS has been most accurate (typical miss 1.62°F); at three days, DWD ICON (1.95°F); at seven days, GEM (Canada) (3.08°F).
The largest standing bias belongs to ECMWF AIFS (AI), which has run cool by about 3.03°F at 3-day lead over this window.
The Spread's own bias-corrected blend scored a 1.32°F typical miss at one day. Its corrections come from the same window it is scored on (in-sample), so read it as a ceiling, not a promise.
The scoreboard
Typical miss (MAE) with the signed bias in parentheses — positive bias means the model ran warm. Days = scored days behind the 1-day number.
| Model | 1-day | 3-day | 7-day | Days |
|---|---|---|---|---|
| ECMWF IFS | 1.6° (-0.2°) | 2.5° (+0.3°) | 5.2° (+0.8°) | 30 |
| NOAA AIGFS (AI) | 1.7° (+0.0°) | 2.1° (-1.0°) | 4.0° (+0.4°) | 30 |
| DWD ICON | 1.8° (+0.3°) | 1.9° (+0.3°) | — | 30 |
| UKMO (UK) | 2.2° (+1.2°) | 3.1° (+1.8°) | — | 30 |
| GEM (Canada) | 2.3° (+1.9°) | 3.0° (-1.6°) | 3.1° (-0.1°) | 30 |
| NOAA GFS | 2.5° (+1.1°) | 3.9° (-2.9°) | 5.6° (-2.2°) | 30 |
| ECMWF AIFS (AI) | 2.6° (-2.5°) | 3.2° (-3.0°) | 4.4° (-2.9°) | 30 |
| NBM (US blend) | 2.1° (+1.2°) | 2.9° (+2.2°) | 5.7° (+5.6°) | 30 |
| Blended (bias-corrected) | 1.3° (-0.0°) | 1.7° (+0.0°) | 3.2° (+0.0°) | 30 |
Method, honestly
Forecasts come from each model's actual archived runs via Open-Meteo's Previous Runs API — what the model said at the time, not a reconstruction. Truth is ERA5 reanalysis daily highs. Rankings cover the models themselves; the two consensus products at the bottom of the table — NBM, which is itself a blend of models, and The Spread's own bias-corrected blend — are shown for comparison, never ranked or named "most accurate" here. The blend's corrections come from the same trailing window it is scored on (in-sample), so treat its score as a ceiling. A rolling 30-day window means these numbers move — that is the point.
Receipts — was the forecast right?
One page per settled date: what every model said as the day approached, what happened, and who was closest.
- Sun Aug 2 6 days out the models said 68–81; it hit 84. ECMWF led (off 0.5°); GEM ran 4° hot.
- Sat Aug 1 5 days out the models said 67–86; it hit 86. GFS led (off 0.1°); AIFS ran 4° cold.
- Fri Jul 31 4 days out the models said 68–84; it hit 76. ICON led (off 0.1°); GFS ran 6° hot.
- Thu Jul 30 3 days out the models said 67–73; it hit 73. GEM led (off 2.6°); AIGFS ran 8° cold.
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The Spread — the forecast spread — is in closed beta. These verification pages are public while the rest is gated.